Using an electronic paper-based screen to improve contrast

ABSTRACT

The invention relates to a projection video system, which comprises a control system for receiving an input video stream. In order to improve the visibility of a projected image so that the projection video system can be satisfactorily used in illuminated rooms, the control system splits the video stream into a first and a second group of image components, 5 and the projection video system further comprises an electronic paper screen system for generating images created by the first group of image components and a projector system for projecting images created from the second group of image components onto the electronic paper screen.

FIELD OF THE INVENTION

The invention relates to a projection television system, and moreparticularly to a method and apparatus for using an electronicpaper-based screen to improve the contrast of the video images projectedby the projection television.

BACKGROUND OF THE INVENTION

A front projection video system displays an image by directing theprojected light from a projector onto a projection screen whichdiffusely reflects the light back into the viewing area. An example of afront projection video system 100 is illustrated in FIG. 1. A videostream, which is to be displayed, is sent to a control system 101. Thecontrol system processes the video stream in known manner and appliesthe processed video stream to a projector 102. The projector projectsthe processed video stream onto a screen 103.

An advantage of front projection systems is that the video projectionscreen 103, which is a thin, wall-mountable unit, is separate from thevideo projector 102, which can be mounted in various positions within aroom. A significant disadvantage of prior front projection video systemsis the need for a darkened room in order to achieve an image withtolerable contrast on the projection screen. A darkened room is requiredbecause light from the projector 102 as well as ambient light in theroom is effectively returned from the screen 103, thereby yielding poorcontrast to the viewer. Under normal lighting conditions in a room, thepicture quality of the front projection video systems is poor comparedto the picture quality of rear projection video systems.

For locations such as hotel lobbies, bars, classrooms, conference rooms,etc., where the placement flexibility of front projection video systemswould make their usage desirable, the darkened conditions that arenecessary for an image of a good quality are totally unacceptable. Thus,there is a need for a front projection video system which has improvedcontrast so that the front projection video system can be satisfactorilyused in illuminated rooms.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to enhance the overall clarity of videoimages projected onto an electronic paper screen by controlling theelectronic paper screen to display high contrast image components of thevideo images being projected by a projection system.

According to one embodiment of the invention, a method and apparatus fordisplaying a video image on an electronic paper screen is disclosed. Aninput video image is divided into a first group of image components anda second group of image components. A first image is generated on theelectronic paper screen, using the first group of image components. Asecond image is projected onto the electronic paper screen, using thesecond group of image components, wherein the second image overlays thefirst image.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings, wherein:

FIG. 1 is a block-schematic representation of a known front projectionvideo system;

FIG. 2 is a block-schematic representation of a known electronic papersystem;

FIG. 3 is a block-schematic representation of a front projection videosystem according to one embodiment of the invention;

FIG. 4 is a block-schematic representation of a control system for afront projection video system according to one embodiment of theinvention;

FIG. 5 illustrates an image projected by the front projection videosystem according to one embodiment of the invention; and

FIG. 6 illustrates an image created by the electronic paper screenaccording to one embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

The invention combines the technology of front projection video systemswith electronic paper to create a new hybrid front projection displaysystem that amalgamates the advantages of both techniques.

The invention relates to addressable, reusable, paper-like visualdisplays, such as “gyricon” (or twisting particle) displays or otherforms of electronic paper, such as particle electrophoretic displays,but the invention is not limited thereto. A gyricon display, also calleda twisting-ball display, rotary ball display, particle display, bipolarparticle light valve, etc., offers a technology for making a form ofelectric paper and other electronically controlled displays. Briefly, agyricon display is an addressable display made up of a multiplicity ofoptically anisotropic particles, with each particle being selectivelyrotatable to present a desired surface to an observer. For example, agyricon display can incorporate “balls” where each ball has two distincthemispheres, one black and one white, with each hemisphere having adistinct electrical characteristic (e.g., zeta potential with respect toa dielectric fluid) so that the ball is electrically as well asoptically anisotropic. The balls are electrically dipolar in thepresence of the fluid and are subject to rotation. A ball can beselectively rotated within its respective fluid-filled cavity, forexample, by application of an electric field, so as to present eitherits black or its white hemisphere to an observer viewing the surface ofthe sheet of electric paper.

A reflective image is formed by the pattern collectively created byindividual black and white hemispheres. By the application of anelectric field addressable in two dimensions (as in a matrix addressingscheme), the black and white sides of the balls are controlled as imageelements (e.g., pixels or subpixels) of a display image. Alternatively,the display may be controlled by shaped electrodes to form one or morefixed images.

The balls are typically embedded in a sheet of optically transparentmaterial, such as an elastomer sheet. A dielectric fluid, such as adielectric plasticizer, is used to swell the elastomer sheet containingthe balls. Through this swelling, the dielectric fluid effectivelycreates a fluid-filled cavity around each ball. The fluid-filled cavityaccommodates the ball and allows the ball to rotate within itsrespective fluid-filled cavity, yet prevents the ball from migratingwithin the sheet.

When an electric field is applied to the sheet over a bead, theelectrical force on the bead overcomes the frictional adhesion of thebead to the cavity wall and causes the bead to rotate. Once rotation iscomplete, each bead will remain in a fixed rotational position withinits cavity. Thus, even after the electric field is removed, thestructures (balls) will stay fixed in position until they are dislodgedby another electric field. This bistability of the beads enables thegyricon display to maintain a fixed image without power. The bistabilityof the gyricon display is beneficial as compared to other types ofdisplays such as a liquid crystal display or a light-emitting diodedisplay which consume energy to maintain the image.

Gyricon displays are not limited to black and white images, as gyriconand other display mediums are known in the art to have incorporatedcolor. Gyricon displays have been developed, incorporating eitherbichromal color, trichromal color, or four quadrant colored balls, orthree or four segmented colored balls. The colored balls can be chargedby adsorption of ions from a liquid onto the ball surface.Alternatively, colored balls can be charged by electret formation byinjection of an external charge into the surface region of the coloredball.

FIG. 2 illustrates a known electronic paper screen 200. The imageinformation is sent to a control system 201. The control system 201analyzes the incoming image data and determines how the electronic paperscreen 202 needs to be charged to create the image. The electronic paperscreen 202 is then charged in an appropriate manner to create the imageon the screen. While electronic paper technology has proved to provideexcellent contrast with low power, electronic paper technology cannotproject a fast moving image.

According to one embodiment of the invention, the input data stream tobe displayed on a screen is split into two component images. The firstcomponent image has coarse-feature, static high contrast imagecomponents which will be extracted and created by the electronic paperscreen. The second component image has fine-feature, fast moving,colored components according to one embodiment of the invention. Thesecomponents of the video image will be generated by the projection imagesystem and projected onto the electronic paper screen. Thus, the secondimage components produced by the projection system will overlay thefirst image components created and displayed by the electronic paperscreen.

A front projection video system 300 according to one embodiment of theinvention will now be described with reference to FIG. 3. The inputvideo stream to be displayed is sent to the control system 301. Theinput video stream can be provided from a multitude of sources such as aDVD, tape, live video feed via cable or wireless links, etc. The controlsystem 301 is illustrated in FIG. 4 in more detail. The input videostream is received by a receiver 401. The input video stream is thensent to an image splitter 403. The image splitter 403 analyzes the inputvideo stream and splits the video stream into the two image componentsdescribed above. Specifically, the image splitter 403 sendsfine-feature, fast moving colored components to a processing system 405which controls the images sent to the projector system 302. The imagesplitter 403 also sends the coarse-feature, static high contrast imagecomponents to the processing system 407 which controls the images sentto the electronic paper screen 304.

For analog images, the stream of images must be digitized or renderedinto a digital form. The standard techniques for image compressionshould be used for this purpose, i.e. MPEG2 encoding. When rendered intoa compressed digital form, the same techniques for splitting the imagecan be used with analog streams as with the digital streams of images.

For digital images, the process of digitization is not necessary as theimage is transmitted in a digital form These digital image formats arecommonly based on the MPEG standard for video compression.Alternatively, they may be propriety formats devised fortelecommunication or computer applications. Thus, they can be stored andmanipulated in a digital form in the processing engine of the displaydevice. To transmit and store the information efficiently, it isnecessary to use efficient compression techniques such as those definedin the MPEG or similar standards.

Compression techniques increase the efficiency of storage by removingredundant details in the spatial and temporal information in the streamof images. This is performed in such a manner that the bandwidth isreduced without drastically reducing the quality of the image perceivedby the human eye. Compression techniques used in MPEG 2 are based on theprinciples of both spatial and temporal compression. Using thesecompression techniques, a simple method of splitting the image for thedescribed invention can be devised, but the invention is not limitedthereto.

For the projected image, the normal compressed image data is processedand projected onto the surface in an unmodified form. However, the imagesent to the electronic paper screen is compressed again to render animage with less temporal and spatial detail.

The first step in this process is to remove the color data from theimage and render a monochrome image. This image is then examined toremove these frames, which include difference data, the so-called P andB-frame in the MPEG 2 streams. These data are removed to leave theI-frames, which contain individually complete static images. A sample ofthese I-frames is then made to match the refresh rate of the electronicpaper screen. If the rate of I-frames is too low, then pseudo I-frameimages should be regenerated using the P and B-frame data, in the usualmanner of MPEG2 decoding. These sets of I-frames are then individuallycompressed to remove spatial details that cannot be rendered on theelectronic paper screen. Such compression techniques are well defined inthe MPEG2 standard. Other compression techniques use similar techniquesfor spatial compression, and are equally valid.

A bounding box can also be added to the final digital image to create a“black border” around the image on the electronic paper screen. This isnecessary to give the human eye a black reference point for the image onthe screen. This enhances the perceived contrast of the image to thehuman eye. The bounding box should frame the images projected on theelectronic paper screen. Spatial positioning of the projected imageshould either arrange this, or the image should be re-positioned on theelectronic screen to achieve the same effect.

As mentioned above, the light-active components are sent to theprojector 302 for projection onto the electronic paper screen 304. FIG.5 illustrates an image being projected onto an electronic paper screen304. The coarse static dark features are sent to the control system 303which drives the electronic paper screen 304 to display these imagecomponents in coordination with the image components being projected bythe projector 302. It will be understood that, optionally, the controlsystem 303 can be removed and the control system 301 can be used tocreate the signals to drive the electronic paper screen 304, and theinvention is not limited thereto. FIG. 6 illustrates an image which iscreated and displayed by the electronic paper screen.

According to another embodiment of the invention, a compensation imagestream can also be created and combined with the image stream beingprojected by the projector on the electronic paper screen. Due to theartifacts of compression introduced by the imaging splitting process,the image displayed by the electronic paper screen will be inferior tothe imaged project by the projection system. These artifacts could bevisible to the human eye if they have a sufficiently long duration or agreater spatial size than the resolution of the display. These effectscan be compensated by reprocessing the projected image to allow forthese artifacts. As illustrated in FIG. 4, a compensation system 409 cancreate the compensation image stream. The compensation image is createdfrom a model of the characteristics of the electronic paper screen. Thiscompensation image is mixed with the image to be projected by theprojector to create a better image on the electronic paper screen.

This compensation is possible by summing the individual I-Frame imagesgenerated for the electronic paper screen with the uncompensatedmonochrome (luminance) I-Frame image generated for the projectionsystem. The difference between the sum of these images and the actualimage will be a difference signal image. These differences signal imagesshould then be added per I-frame to the projection system image I-framesto create the compensated projection image sequence. P and B-framesshould then be created for the projection image sequences on the basisof the compensated I-frames, and displayed in the normal fashion ofMPEG2 images.

Where the match between the electronic paper screen and the projectionsystem in terms of definition and other image aspects is similar, thecompensation image will have little impact on the overall image.However, to reduce costs and improve flexibility, the screen and theprojection system may not be matched in terms of display attributes.Specifically, the screen could be very coarse in terms of spatial andtemporal resolution. These characteristics of the screen can be providedby the processing algorithms based on a model of the interaction of thehybrid projection system, and of the sequence of images.

It will be understood that the different embodiments of the inventionare not limited to the exact order of the above-described steps as thetiming of some steps can be interchanged without affecting the overalloperation of the invention. Furthermore, use of the verb “comprise” andits conjugations does not exclude other elements or steps, and use ofthe indefinite article “a” or “an” does not exclude a plurality of suchelements or steps, while a single processor or other unit may fulfillthe functions of several of the units or circuits recited in the claims.

1. A projection video system, comprising: a control system (301) forreceiving an input video stream, wherein the control system splits thevideo stream into a first and a second group of image components; anelectronic paper screen system (303, 304) for generating images createdby the first group of image components; a projector system (302) forprojecting images created from the second group of image components ontothe electronic paper screen.
 2. The projection video system as claimedin claim 1, wherein said first group of image components hascoarse-feature, static high contrast image components.
 3. The projectionvideo system as claimed in claim 1, wherein said second group of imagecomponents has fine-feature, fast moving colored components.
 4. Theprojection video system as claimed in claim 1, further comprising: acompensation unit (409) for creating a compensation signal which iscombined with the second group of image components before beingprojected onto the electronic paper screen.
 5. The projection videosystem as claimed in claim 4, wherein said compensation signalcompensates for different display attributes between the projector andthe electronic paper screen.
 6. The projection video system as claimedin claim 4, wherein said compensation signal is added to each I-frame ofthe second group of image components.
 7. The projection video system asclaimed in claim 4, wherein said compensation signal is generated bysumming individual I-frame images generated for the first group of imagecomponents with an uncompensated monochrome I-frame image generated forthe projection system, subtracting the summed signal from the actualimage.
 8. The projection video system as claimed in claim 1, whereinsaid electronic paper screen generates a bounding box around the imageon the electronic paper screen.
 9. The projection video system asclaimed in claim 8, wherein the bounding box is a black border.
 10. Amethod of displaying a video image on an electronic paper screen, themethod comprising the steps of: dividing an input video image into afirst group of image components and a second group of image components;generating a first image on the electronic paper screen, using saidfirst group of image components; and projecting a second image onto theelectronic paper screen, using said second group of image components,wherein the second image overlays the first image.
 11. The method asclaimed in claim 10, wherein said first group of image components hascoarse-feature, static high contrast image components.
 12. The method asclaimed in claim 10, wherein said second group of image components hasfine-feature, fast moving colored components.
 13. The method as claimedin claim 10, further comprising the step of: creating a compensationsignal which is combined with the second group of image componentsbefore being projected onto the electronic paper screen.
 14. The methodas claimed in claim 13, wherein said compensation signal compensates fordifferent display attributes between the projector and the electronicpaper screen.
 15. The method as claimed in claim 13, wherein saidcompensation signal is added to each I-frame of the second group ofimage components.
 16. The method as claimed in claim 13, wherein saidcompensation signal is generated by summing individual I-frame imagesgenerated for the first group of image components with an uncompensatedmonochrome I-frame image generated for the projection system,subtracting the summed signal from the actual image.
 17. The method asclaimed in claim 10, wherein said electronic paper screen generates abounding box around the image on the electronic paper screen.
 18. Themethod as claimed in claim 10, wherein the bounding box is a blackborder.
 19. The method as claimed in claim 10, further comprising thestep of: compressing the first group of image components and the secondgroup of image components after dividing the input video image.
 20. Themethod as claimed in claim 19, further comprising the step of:compressing said first group of image components a second time to removespatial details that cannot be rendered on the electronic paper screen.